Processing aids for hydroxy-terminated polybutadiene propellant(u)

ABSTRACT

This patent describes a novel solid propellant formulation containing a hydroxy-containing polybutadiene polymer, a solid oxidizing agent and having a high solids content; the improvement wherein the propellant has an increased pot life and reduced viscosity by the incorporation therein of a small effective amount of a compound selected from the group consisting of those having the generic formula:   WHEREIN R is hydrogen, omega -hydroxy alkyl, phenyl, cyclohexyl,   R&#39;&#39; is an omega -hydroxy alkyl or hydroxyphenyl, R&#39;&#39;&#39;&#39; is alkyl, and n is an integer from 1 to about 20; or   WHEREIN R&#39;&#39;&#39;&#39;&#39;&#39; is an alkyl or aryl group and m is an integer from 1 to about 20. This invention also includes the method of forming said formulation, and casting and curing the same to form a solid propellant.

United States Patent 1191 Mastrolia et al.

[451 Apr. 2, 1974 I PROCESSING AIDS FOR HYDROXY-TERMINATED POLYBUTADIENEPROPELLANT(U) [73] Assignee: Aerojet General Corporation, El

Monte, Calif.

22 Filed: Aug. 19,1970

[2i] Appl. No.: 76,343

[52] US. Cl 149/19, 149/20, 149/38, 149/44, 149/76 [51] Int. Cl C06d5/06 [58] Field of Search 149/19, 60, 76, 83, 20,

[56] References Cited I UNITED STATES PATENTS 3,666,575 5/1972 Fisher149 19 3,677,840 7/l972 Shaw et al. 149/19 3,532,567 10/1970 Winkler etal. l49/19 3,399,088 8/1968 Christian et a1. 149/19 3,529,042 9/1970Lippert l49/l9 X 3,305,523 2/1967 Burnside 149/19 X PrimaryExaminer-Benjamin R. Padgett Assistant ExaminerE. A. Miller Attorney,Agent, or Firm-Mark C. Jacobs [57] ABSTRACT This patent describes anovel solid propellant formulation containing a hydroxy-containingpolybutadiene polymer, a solid oxidizing agent and having a high solidscontent; the improvement wherein the propellant has an increased potlife and reduced viscosity by the incorporation therein of a smalleffective amount of a compound selected from the group consisting ofthose having the generic formula:

RNR,

wherein R is hydrogen, al-hydroxy alkyl, phenyl, cyclohexyl,

R is an w'hydroxy alkyl or hydroxyphenyl, R" is alkyl, and n is aninteger from 1 to about 20; or

wherein R is an alkyl or aryl group and m is an integer from 1 to about20. This invention also includes the method of forming said formulation,and casting and curing the same to form a solid propellant.

4 Claims, 2 Drawing Figures ZATENTED APR 2 i974 'SHEU 2 BF 2 N dfINVENTORS EDMUND J. MASTROLIA HARRY J. MICHIGIAN ATTORNEYS PROCESSINGAIDS FOR HYDROXY-TERMINATED POLYBUTADIENE PROPELLANT(U) BACKGROUND OFTHE INVENTION Most methods of improving propellant flow propertiesinvolve the use of surfactants which coat the surface of the propellantsolids, do not become part of the crosslinked binder and, hence, disruptthe solids-binder bond causing a deterioration of the propellantmechanical behavior. This invention reduces the viscosity and extendsthe pot life of hydroxy-terminated polybutadiene composite propellantswhile improving the resistance of the binder towards oxidative attack.The improvements in pot life and viscosity will allow additional timefor motor casting after the addition of the curing agent, thus providinggreater assurance of void free castings and, hence, improved grainintegrity. In a preferred embodiment, this invention reduces theviscosity and extends the pot life of high solids loadinghydroxy-terminated polybutadiene propellants and simultaneously providesan enhancement of propellant mechanical behavior over a wide temperaturerange.

SUMMARY OF THE INVENTION Briefly, this invention comprises a novel solidpropellant formulation containing a hydroxy-containing polybutadienepolymer, a solid oxidizing agent and having.

a high solids content; the improvement wherein the propellant has anincreased pot life and reduced viscosity by the incorporation therein ofa small effective amount of a compound selected from the groupconsisting of those having the generic formula:

wherein R is hydrogen, m-hydroxy alkyl, phenyl, cyclohexyl,

R is an w-hydroxy alkyl or hydroxyphenyl, R" is alkyl, and n is aninteger from 1 to about 20; or

i r l /mlz wherein R' is an alkyl or aryl group and m is an integer from1 to about 20.

It is an object of this invention to provide a novel propellantformulation having increased pot life and reduced viscosity.

More specifically, it is an object of this invention to provide apropellant of increased pot life and reduced viscosity having a highsolids loading.

It is a further object to improve the manufacture and casting ofpropellants based on hydroxy-terminated polybutadiene binders, andpreferably based on the polyurethane polymer resulting from the reactionof a hydroxy-terminated polybutadiene and an organic diorpolyisocyanate.

In a preferred embodiment, it is an object of this invention to providea propellant having improved mechanical properties in the cured statetogether withrimproved pot life and reduced viscosity in the uncuredstate.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Compounds containing thegeneral structure wherein R' and m are as defined above, are effectiveprocessing aids in the preparation of high solids loadinghydroxy-terminated polybutadiene propellants. Specifically, ammoniumperchlorate propellants prepared with hydroxy-terminated polybutadieneprepolymers, cured with aliphatic or aromatic diisocyanates orpolyisocyanates and plasticized with hydrocarbon or ester species, showa substantial improvement in viscosity characteristics in the presenceof small quantities of these materials.

This invention improves the processing characteristics of high solidsloading hydroxy-terminated polybutadiene propellants and simultaneouslyprovides improvements in the uniaxial tensile properties of thesepropellants over the temperature range of to +F by the use of thecompounds having the formula wherein R is as defined above. Compoundsfound to provide this enhancement in flow properties and mechanicalbehavior belong to a family of substituted alkanol and hydroxyphenylamines. The most dramatic improvements in both propellant processing andmechanical property behavior was obtained with either diethanolamine ortriethanolamine.

While not bound by any theory, it is believed that the compounds of theabove formulae react with the ammonium perchlorate and/or ammoniumnitrate oxidizer, liberating ammonia and tightly adhere to the surfaceof the oxidizer.

The hydroxy species present in the amines react with the isocyanatecuring agent, thus forming a firm bond between the solid oxidizer andthe crosslinked binder.

Compounds of this type contain at least two functional groups (e.g., OHspecies) which form a complete polymer network. The improvement in flowproperties (wetting action) achieved with the alkanol amines occurs byproviding a bridge between the polar solid oxidizer and the essentiallynon-polar binder, thus resulting in greater compatibility between thebinder components and the solid oxidizer.

The oxidizer-binder bond which is formed and is believed to account forthe mechanical property improvements, is assured by the completion ofthe above reaction with hydroxyl species.

Thiodipropionate esters of the general structure where R' is either analkyl or aryl radical, also reduce the initial viscosity and extend thepot life (as determined by the time between curing agent addition andtime when the propellant viscosity at +135F reaches 30,000 poise) ofsolid rocket propellants based on hydroxy-terminated polybutadienebinders.

In general, the propellant formulations of this invention containinorganic oxidizingagents such as ammonium perchlorate, ammonium nitrateand potassium perchlorate; organic oxidizers such as cyclotrimethylenetrinitramine and cyclotetramethylene tetranitramine; metallic fuels suchas powdered aluminum, beryillium, boron and magnesium; plasticizers suchas hydrocarbon oils and high molecular weight esters; and curing orcrosslinking agents such as toluene diisocyanate, hexamethylenediisocyanate and isophorone diisocyanate. The solids content of thesepropellants may range up to 92 percent, where these solids consist ofthe oxidizer(s) plus the metallic fuel(s).

The effect of the compounds of the above formulae is to make the solidsand the polymeric fuels more compatible, resulting in better wetting ofthe solids by the liquids, and hence, better flow properties of theslurries. A typical example of the improvements in the viscosity of ahighly loaded hydoxy-terminated polybutadiene propellant is shown inFIG. 1 for the thiodipropionate esters di-2-ethylhexyl-thiodipropionate,dilauryl thiodipropionate, and distyryl thiodipropionate. In all cases,regardless of whether the structure contains aromatic or alkyl groups, asimilar effect of reduction of propellant viscosity is achieved. Asshown below, this improvement in flow characteristics is achieved with-(C) Propellant number 1 2 3 4 5 1O Ingredient weight percent:

Nmcio. 68.00 68. as oo 68. 00 68.00 Powdered aluminum 18. 00 1& 00 18.00 18.110 18. 00 F820: 1.00 1.00 1.00 1.00 1 0O Hydroxy-terminated poly-4 butadiene. 7. 700 7.700 7.700 7. 812 Triethanolamine. 037 037 037Toluene diisocyanate 453 .453 453 443 1 Dioetyl azelate 4. 410 4. 410 4.410 4. 445

. y z rfirnap y -pphenylene diamine 0.20 0.20 0.20 0.20 0. 200Ditridecyl thiodipropionate 0. 100 Di-2-ethy1hexylthi0dipropionate 0.20Dilauryl thiodipropionate 0. Distyryl thiodipropionate 0. 20

20 A vflflwflw V W (C) Propellant number 6 7 8 9 Ingredient, weightpercent:

NH4C10 68.00 68. 00 68.00 68. 0O Powdered aluminum 18. 00 18. 00 18. 0018.00 F6203 1.00 1.00 1. 00 1.00 Hydroxy-temilnated polybutadiene... 7.761 7. 761 7. 418 7. 690 Trinthannlaminn 037 Diethanolamine. 0. 037Bis-hydroxy ethylcyclohexylamine 0.276

Bls-cyanoethyl dlhydroxy-propylamine.. 0.074 Toluene diisocyanate 0. 457457 0. 56 0. 591 Dloctyl azelate 4. 445 4. 445 4. 445 4.445Sym-dl-fl-naphthyl-p-phenylene dlamlne 0. 20 0. 20 0. 200 0. 200Ditrldecyl thiodlproplonate 0.10 0.10 0.100 0. 100 a Shore A BatchThiodipropionate ester, Hardness No 1 None (control) 2di-Z-ethylhexylthiodipropionate 44 3 dilauryl thiodipropionate 56 4distyryl thiodipropionate.

The improvement in propellant processing that can be achieved with thetertiary amine bonding agents is shown in FIG. 2. The best results areobtained with either diethanolamine, triethanolamine, cyclohexylsubstituted diethanolamine, or combinations of the above three withother bonding agents. This can be seen by comparing the viscositybuildup of Propellant 5 which contains no bonding agent to Propellant 6,Propellant 7 and Propellant 8 which contain diethanolamine,triethanolamine and cyclohexyl substituted diethanolamine. Also,comparison of the viscosity characteristics of Propellant 6 topropellants containing any of the above three bonding agents incombination with other bonding agents also demonstrates superiorprocessing properties for the latter systems.

The mechanical behavior of these propellants over a wide temperaturerange (as measured by both uniaxial tensile properties and in strainevaluation cylinders) is shown in the following table.

V 'rLABLn EU) iaFfiisaxaeseswmFoam w'r PERCENT SOLIDS PROPELLANTS +160to -75 F., thermal cycling Unlaxlal tensile properties strain, percentTDI Test level, temp., m c e E.,, Sec. 1st 5th 10th Batch number Bondlngagent eq. p.s.i. percent percent p.s.l No. cycle cycle cycle Propellant:

+77 95 3a 34 37s 1 F F F 6 Diethanolamme t. 65 40 205 41 53 1,360 2 F FF -75 366 40 52 4,925 3 22. 5 F F 4 21. 1 F F +77 132 32 32 568 1 F F E7 Trletbanolamine A. 70 40 260 49 53 1, 436 2 F F F -75 510 45 56 5, 3723 22. 2 22. 22. 2 4 21.9 21. 9 F +77 66 36 40 267 1 F F F s Bis-hydroxyethyl cyclo- 70 -40 163 18 58 1,578 2 F F F hexylamme. 75 364 9 52 6,617 3 F F F 4 21. 4 23. 0 F +77 68 29 32 320 1 F F F 9 None (control) 7540 167 18 31 1,562 2 F F F --75 302 12 32 4,870 3 F F F 4 22, F F +77109 37 38 390 1 F F F Bls-eyanoethyl dihydroxy- 73 -40 235 33 36 1,857 2F F F propylamine. -75 417 31 44 4, 903 3 22. 8 22. 8 F 4 23. 0 21. 423. 0

The effect of the various bonding agents on low temperature (-40F and75F) mechanical properties can be seen by comparing the results frombatch Propellant 5 (no bonding agent) to the results from the otherpropellant batches. A dramatic improvement in the uniaxial tensileproperties over the entire temperature range can be seen uponincorporating bonding agents into the propellant formulation. The bestresults are obtained with either diethanolamine or triethanolamine,(compare batches Propellant 7, Propellant 9 and Propellant 6 toPropellant 5).

The improvement in thermal cycling strain capability can be seen bycomparing Propellant 5 (no bonding agent) to Propellant 7(triethanolamine bonding agent). With the triethanolamine bonding agentthe thermal cycling capability (160F to -75F), was increased from 22.5%for one cycle in the propellant containing no bonding agent to 10 cyclesat 22.2% in the propellant containing triethanolamine.

Having fully described the invention, it is intended that it be limitedonly by the lawful scope of the appended claims.

We claim:

1. A novel solid propellant formulation comprising a hydroxy-containingpolybutadiene, a solid oxidizing agent and having a high solids content;the improvemeit'tmieifihe propellant has H'ifiieaed pot life and reducedviscosity by the incorporation therein of a small effective amount ofdi-2-ethylhexylthiodipropionate.

2. A novel solid propellant formulation comprising a hydroxy-containingpolybutadiene, a solid oxidizing agent and having a high solids content;the improvement wherein the propellant has an increased pot life andreduced viscosity by the incorporation therein of a small effectiveamount of dilauryl thiodipropionate.

3. A novel solid propellant formulation comprising a hydroxy-containingpolybutadiene, a solid oxidizing agent and having a high solids content;the improvement wherein the propellant has an increased pot life andreduced viscosity by the incorporation therein of a small effectiveamount of distyryl thiodipropionate.

4. A novel solid propellant formulation comprising a hydroxy-containingpolybutadiene, a solid oxidizing agent and having a high solids content;the improvement wherein the propellant has an increased pot life andreduced viscosity by the incorporation therein of a small effectiveamount of a dithiodipropionate selected from the group consisting ofditridecyl thiodipropionate, di-2-ethylhexyl thiodipropionate, dilaurylthiodipropionate, and distyryl thiodiopropionate.

2. A novel solid propellant formulation comprising a hydroxy-containingpolybutadiene, a solid oxidizing agent and having a high solids content;the improvement wherein the propellant has an increased pot life andreduced viscosity by the incorporation therein of a small effectiveamount of dilauryl thiodipropionate.
 3. A novel solid propellantformulation comprising a hydroxy-containing polybutadiene, a solidoxidizing agent and having a high solids content; the improvementwherein the propellant has an increased pot life and reduced viscosityby the incorporation thErein of a small effective amount of distyrylthiodipropionate.
 4. A novel solid propellant formulation comprising ahydroxy-containing polybutadiene, a solid oxidizing agent and having ahigh solids content; the improvement wherein the propellant has anincreased pot life and reduced viscosity by the incorporation therein ofa small effective amount of a dithiodipropionate selected from the groupconsisting of ditridecyl thiodipropionate, di-2-ethylhexylthiodipropionate, dilauryl thiodipropionate, and distyrylthiodiopropionate.